Polymer nanocomposites (PNCs) are hybrid materials incorporating organic or inorganic nanoparticles (NPs) with at least one dimension in the submicron scale. Over the last two decades, these materials have drawn a remarkable attention due to their central role in industrial formulations and technological applications, extending from food packaging to smart coatings. Incorporating nanoparticles (NPs) to a polymer matrix can significantly alter the conformation and the mobility of the polymer chains in their proximity. Moreover, understanding the delicate balance between the enthalpic and entropic interactions is crucial to control and predict the ability of NPs to diffuse and disperse in the polymer matrix. The impact of these interactions on the structure and the dynamics of polymer chains and NPs is fully revealed in how a number of macroscopic properties changes, justifying the high interest on these materials for industrial applications. In this thesis, the impact on the structure, dynamics, viscosity and thermal conductivity of a number of microscopic properties is investigated by performing Molecular Dynamics (MD) simulations. Specifically, the PNC is represented by a coarse-grained model of a melt of linear homopolymer chains containing spherical NPs. Throughout this work, a number of parameters are modified in order to unveil possible patterns in the PNC’s performance. To this end, this work focuses on the consequences of modifying the NP size dispersity, NP-polymer chain relative size, and chains’ degree of stiffness. Four theoretical models describing the diffusivity of NPs, three of which include nano-scale corrections, have been averaged to study the dependence of dilute NPs’ diffusivity on the NP polydispersity index. By comparing these models to the simulation results at different degrees of polydispersity, it is possible to obtain a more complete picture of their validity as compared to the monodisperse case. Regarding the diffusion of polymer chains, simulation results were in good agreement with the experimental results previously obtained by Composto and coworkers (Soft Matter 2012, 8, 6512), which relate the chains’ diffusivity to the average interparticle distance. As far as the transport properties are concerned, they show a weaker dependence on the polydispersity index. By contrast, results on viscosity and thermal conducitivity show that they are conditioned by the polymer-NP specific interfacial area and the inverse average mass, respectively. These results are in good agreement with previous experimental results. A deeper examination of this intriguing deviation from viscosity predictions in traditional composites, reveals a non-trivial combination of thickening and thinning effects contributing to the final viscosity of the PNC. This thesis also address the influence of the chains’ stiffness on the dynamical and viscous behaviour. An isotropic-to-nematic phase transition is observed, regardless of the NP-monomer interactions, below which a monotonic increase of both properties is observed, whereas orientationally ordered systems dramatically modify them, resulting into a steep increase or a smooth decrease depending on the direction in which they are measured.

Herein, we study the contact damage performance of two armour ceramics, alumina and silicon carbide, with varying microstructures and one particle-reinforced ceramic nanocomposite, alumina/silicon carbide, in an attempt to understand the microstructural mechanisms that affect plasticity and cracking under quasi-static and dynamic conditions. Quasi-static contact damage was imitated using Vickers indentation over a varying load regime. Numerical analysis of the indentation size effect, performed using the proportional specimen resistance model, allowed the contributions of plastic deformation and cracking to be separated into two individual values. In all three samples, higher levels of surface energy were found to correlate with increased amounts of cracking per unit area of indentation impression. Analytical modelling of crack initiation during Vickers indentation together with quantitative measurements of surface flaw populations revealed that such an increase in cracking damage was the result of higher densities of larger flaws. The hardness of the monolithic ceramics was found vary based on grain size and porosity levels, a smaller average grain size and lower porosity levels resulting in higher hardness values. In the nanocomposite materials, hardening was found to occur with further additions of silicon carbide nanoparticles. Such an effect has been attributed to the increased dislocation densities, as measured using Cr3+/Al2O3 fluorescence spectroscopy, and the impedance of dislocation movement within the lattice due to the presence of silicon carbide nanoparticles. In order to simulate dynamic contact damage, a low velocity, scaled-down drop-weight test was designed and developed. The dynamic contact damage resistance was determined based on the depth of penetration of a blunt indenter. In the monolithic ceramics, the indenter penetration was found to be shallower in materials of higher hardness. However, the nanocomposite materials displayed an opposing trend, the indenter penetration becoming deeper in the samples of higher hardness. The macro-scale fracture patterns produced during drop-weight impacts were seen to vary based on flaw populations and indenter penetration. In certain microstructures, extensive micro-cracking was also observed.

My PhD thesis work is to design, synthesize, and characterize inexpensive and reliable nanocomposites for the photovoltaic (PV) devices. Photovoltaic materials utilized in our studies were synthesized using simple and inexpensive methods. The material properties were tailored and optimized to improve the optical absorption and charge transport properties. The PV cells fabricated with these materials exhibited improved power conversion efficiencies (PCE). The origin of charge generation and charge transfer was studied using different photoactive materials such as CdSe quantum dots (QDs), perylene-3, 4, 9, 10-tetracarboxylic-3, 4, 9, 10-dianhydride (PTCDA), poly(3-hexylthiophene) (P3HT), multiwalled carbon nanotubes (MWCNTs), multilayer graphene (MuLG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM).

It is common knowledge that water is one of the basic needs for human beings. However, the consumption of contaminated water can lead to waterborne diseases and fatalities. It is, therefore imperative to constantly monitor the quality of potable water. There are numerous technologies used for water quality monitoring. These technologies are relatively effective however these tests are expensive and complex to use, which then require experienced technicians to operate them. Other tests are not rapid, making consumers of water susceptible to waterborne diseases. In this study, dye-doped, surface functionalized silica nanoparticles (SiNPs) and surface-functionalized magnetic nanocomposites (MNCs) were proposed as materials that can be applied in order to reduce the time taken to get results as well as to make the processes less complex and portable. The aim of this study was to synthesize and characterize surface functionalized dye-doped SiNPs and surface functionalized MNCs for detection and preconcentration of in water. Additionally, proof of concept had to be shown using the synthesized materials. SiNPs were the materials of choice due to their easily functionalized surfaces and their strong optical properties. SiNPs are photostable and they do not leach in solution due to the inert nature of the silica matrix in aqueous media. MNCs were chosen as materials of choice for preconcentration of E. coli in water because they are easy to synthesize and they can be applied in various biological applications due to their functional groups. SiNPs were synthesized using the water-in-oil microemulsion. The SiNPs were further functionalized with amine and carboxyl groups and avidin. Thereafter, they were bioconjugated with biotinylated anti-E. coli antibodies. The pure and surface functionalized SiNPs were characterized using ATR-FTIR spectroscopy, FE-SEM, HR-TEM, Zeta Sizer, UV-vis spectroscopy and spectrofluorometry. The application of the dye—doped surface functionalized SiNPs in E. coli detection was characterized using the fluorescence plate reader. The SiNPs were spherical and uniform in size. They increased in size as they were being functionalized, ranging from 21.20 nm to 75.06 nm. The SiNPs were successfully functionalized with amine and carboxyl groups as well as with avidin and antibodies. Two methods were investigated for carboxyl group attachment (direct and indirect attachment) and the direct attachment method yielded the best results with a surface charge of -31.9 mV compared to -23.3 mV of the indirect method. The dye loading was found to be 1% after particle synthesis. The optical properties of the Ru(Bpy) dye were enhanced 3 fold when they were encapsulated in the Si matrix. The SiNPs were binding to the E. coli cells and enabled detection. MNCs were synthesized through in-situ polymerization. The MNCs were characterized using ATR-FTIR spectroscopy, SEM, TEM and XRD. The MNCs were successfully functionalized with carboxyl groups. The increase in size of the nanocomposites as seen in SEM images proved that the Fe3O4 was successfully encapsulated in the polymer matrix. The MNCs were proven to be magnetic by a simple magnetism test whereby they were separated in an aqueous solution using an external magnetic field. The antibody-labelled MNCs were binding to the E. coli cells as shown in TEM images. E. coli cells were removed from water at varying concentrations of 1x106 CFU/mL to 1x109 CFU/mL at 10 mL volumes. This study has demonstrated that dye-doped SiNPs amplify the signal of E. coli cells using fluorescence. The study has also demonstrated that the MNCs can be applied in sample preconcentration and enrichment for E. coli detection. However, further studies should investigate and optimize the combination of the two techniques in a point of use device for water quality testing of 100 mL-samples as per the requirement of the SANS 241 standard. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

As resinas termorrígidas são uma classe de polímeros que devido à reação de reticulação deveriam apresentar uma única cadeia molecular de peso infinito, no entanto, questionamentos sugerem que a formação da rede tridimensional é não-homogênea. Atualmente, devido aos avanços obtidos pela nanotecnologia, torna-se possível uma abordagem diferenciada na modificação química de polímeros como a resina epoxídica. Neste trabalho, foram preparados nanocompósitos adicionando diferentes teores do oligômero poliédrico de silsesquioxano (POSS) n-fenilaminopropil na resina epoxídica. Foi substituindo 1, 5 e 10 por cento em massa (% m.) do agente de reticulação trietilenotetramina (TETA) por POSS. Esta modificação foi realizada com o objetivo de promover maior concentração de interligações nas interfaces das regiões nodulares, descritas como imperfeições ou descontinuidades que ocorrem pela cura não-homogênea da resina. Através da morfologia e da análise do teor de gel, foi evidenciada boa dispersão e melhoria na homogeneidade da rede tridimensional da resina acima de 5 % m. de POSS e aumento da fração gel nos nanocompósitos comparados com a resina epoxídica pura. Na realização de análises de difração de raio-x (DRX) foi visto que a adição do POSS aumentou a distância média entre as cadeias da resina. Foi realizada análise dinâmico-mecânica (DMA) no modo não-isotérmico e por varredura de frequência no modo isotérmico. Pelo modo não-isotérmico os resultados demonstraram que o POSS deslocou a Tg para temperaturas maiores e não alterou significativamente a densidade de ligações cruzadas da resina epoxídica. O modo isotérmico foi utilizado para a determinação de parâmetros das equações de Williams-Landel-Ferry (WLF) e Vogel-Fulcher-Tammann (VFT). Foi calculada a distribuição dos espectros de relaxação H(t) e retardação L(t) molecular através dos módulos de armazenamento e perda obtidos pelo modo isotérmico no DMA. Os parâmetros WLF e VFT demonstraram que a incorporação do POSS ao mesmo tempo em que aumentou a Tg, reduziu a energia de ativação de movimentação segmentar e tornou a resina epoxídica mais forte estruturalmente. A redução da energia de ativação foi associada com a redução das forças de interação intermolecular, enquanto que a redução da fragilidade foi associada ao fato do POSS ser capaz de interligar as interfaces de regiões nodulares. Os espectros H(t) e L(t) mostraram que o pico de relaxação associado aos nódulos formados no processo de reticulação desapareceu. A determinação da capacidade calorífica (Cp) e do excesso de entropia (Sex) através de análises de calorimetria exploratória diferencial modulada (MDSC) demonstrou que o POSS é capaz de minimizar as flutuações de calor ao longo da microestrutura da resina epoxídica. A minimização das flutuações térmicas e a alteração dos tempos de relaxação demonstram que a adição do POSS é eficiente em termos de minimização de imperfeições na microestrutura da resina epoxídica. / The thermosetting resins are a class of polymers that due to the crosslinking reaction should present a single chain with infinite molecular weight; however, questions suggest that the formation of three-dimensional network is non-homogeneous. Today, due to advancements in nanotechnology, became possible a differentiated approach in the chemical modification of polymers such as epoxy resin. In this work, nanocomposites with different contents of the polyhedral oligomeric silsesquioxane (POSS) n-phenylaminopropyl in epoxy resin were prepared. It was substituted 1, 5 and 10 weight percent (wt%) of the crosslinking agent, triethylenetetramine (TETA), for POSS. This modification was performed in order to promote greater concentration of interconnections at the interfaces of the regions described as nodular imperfections or discontinuities that arise due to inhomogeneous cure of the resin. Through the morphology and the gel content analysis was observed good dispersion and improvements in the uniformity of three-dimensional network of the resin up till 5 wt% of the POSS and increase in the gel fraction of the nanocomposites compared with pure epoxy resin. X-ray diffraction (XRD) showed that the POSS promoted an increase in distance between chains of the resin. Dynamic-mechanical analysis (DMA) was performed in non-isothermal mode and a frequency sweep in the isothermal mode. By non-isothermal mode the results showed that the POSS shifted the Tg to higher temperatures and does not modify the crosslink density. The isothermal mode was used to determine the parameter of the Williams-Landel-Ferry (WLF) and Vogel-Fulcher-Tammann (VFT) equations. The distribution of the relaxation H(t) and retardation L(t) spectra was calculated through the storage (E') and loss (E'') modulus obtained by the DMA isothermal mode. The WLF and VFT parameters showed that the incorporation of POSS at the same time increased the Tg reduced the activation energy of segmental motion and made the epoxy resin structurally stronger. The reduction in the activation energy was associated with reduced intermolecular forces whereas the decrease in the structural fragility is associated with the fact that the POSS be able to interconnect the interfaces of the nodular regions. The H(t) and L(t) spectra showed that the nodules formed in the crosslinking process disappeared. The determination of the heat capacity (Cp) and excess entropy (Sex), analyzed by modulated differential scanning calorimetry (MDSC), showed that POSS is capable of minimizing fluctuations of heat along the microstructure of the epoxy resin. The reduction of thermal fluctuations and change in the relaxation times shows that the POSS addition is efficient to minimize imperfections in the microstructure of the epoxy resin.

No fim do século XX cresceu o interesse por materiais com potencial para aplicação na área da nanotecnologia. Um destes materiais é o grafeno (alótropo do carbono da espessura de um átomo), indicado para aplicações que exploram desde propriedades ópticas até mecânicas. Todavia, os métodos de produção estabelecidos até o momento geram normalmente um produto com alto grau de defeitos estruturais. Por isso, o objetivo deste estudo foi desenvolver um método mais brando para obtenção de grafeno, por meio do desenrolamento de nanotubos de carbono (NTC) de parede múltipla na presença de líquidos iônicos (LI) (que possuem caráter lubrificante e estabilizador) e adicioná-lo à resina epoxídica para avaliar seu efeito nas propriedades do nanocompósito. A metodologia consistiu em definir a rota a que a mistura NTC:LI (bis(trifluorometanosulfonil)imidato de 1-n-butil-3-metilimidazólio – BMImNTf2), na proporção 1:10, deveria ser submetida e depois avaliar variações para validação do método (alteração de temperatura, solventes – LI BMImCl e tolueno e nanocarga – grafite). As misturas de grafeno-NTC/LI produzidas foram adicionadas na proporção de 0,1% em massa de grafeno-NTC à resina epoxídica. A caracterização das misturas se deu pelas técnicas de microscopia eletrônica de transmissão (MET), espectroscopia Raman e microscopia de força atômica (AFM), e dos nanocompósitos, também por microscopia eletrônica de varredura (MEV), análise termogravimétrica (TGA), calorimetria diferencial exploratória (DSC), infravermelho (IV) análise dinâmico-mecânica (DMA) e ensaios mecânicos. A morfologia observada em MET e AFM evidenciou que a rota em que a mistura permaneceu 3 h em aquecimento e agitação magnética sob vácuo e 3 h sob sonificação resultou em grafeno de algumas camadas. Os resultados de Raman mostraram que foi produzido grafeno de boa qualidade, baseando-se na razão ID/IG. Nos nanocompósitos, confirmou-se que BMImNTf2 mantém as folhas de grafeno abertas. Já com BMImCl a morfologia dos NTC permanece inalterada, mas seu grau de emaranhamento é diminuído pela ação lubrificante deste LI, o que reflete em melhoria na resistência ao impacto. Os NTC sem a presença de um LI de forma geral não conferiram melhoria à matriz polimérica (ex: queda de 35% na dureza). / In the late twentieth century, the interest in materials with potential application in the nanotechnology´s field has increased. One of these materials is graphene (carbon allotrope of a single atom thickness), suitable for applications, which exploit properties such as optical or mechanical. However, the methods developed up to now to obtain graphene usually generate a product with high degree of structural defects. Therefore, the aim of this study was to produce graphene sheets through a milder route of unrolling multi-walled carbon nanotubes (CNT) in ionic liquids (IL; which have a lubricating and stabilizing character) and to add it to an epoxy resin to evaluate its effect on the nanocomposite properties. The methodology consisted of defining the route through which the 1:10 mixture of CNT:IL (1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate - BMImNTf2) should be submitted, and then evaluate possible variations for validating the method (change in temperature, solvents - toluene and IL BMImCl and nanofiller - graphite). The produced graphene-CNT/IL mixtures were added at 0.1% by weight of graphene-CNT to epoxy resin. Characterization of the graphene/IL mixtures was done by transmission electron microscopy (TEM), Raman spectroscopy and atomic force microscopy (AFM), and the nanocomposites also by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamical mechanical analysis (DMA) and mechanical tests. The morphology observed using TEM and AFM showed that the route based on 3 h under heating, stirring and vacuum, followed by 3 h of sonication leads to CNT unrolling. Raman spectra showed that the produced graphene was of good quality, based on the low ID/IG ratio. In the nanocomposites, CNT unrolling was confirmed when IL BMImNTf2 was used, yielding reasonable property improvements. In the case of IL BMImCl, the unrolling of the CNT did not occur, but the lubricant effect of the IL decreased the degree of entanglement, which increased its impact strength. Differently, the non-treated CNT generally reduced the properties of the polymer matrix, e.g. a 35% drop in hardness.

Submitted by RENAN DA SILVA FERNANDES null (r.feernandes@yahoo.com.br) on 2016-05-06T16:01:09Z No. of bitstreams: 1 Dissertacao Renan.pdf: 4246909 bytes, checksum: 19c74f241fc5b3a706f6c977c778131d (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-05-09T19:06:55Z (GMT) No. of bitstreams: 1 fernandes_rs_me_ilha.pdf: 4246909 bytes, checksum: 19c74f241fc5b3a706f6c977c778131d (MD5) / Made available in DSpace on 2016-05-09T19:06:55Z (GMT). No. of bitstreams: 1 fernandes_rs_me_ilha.pdf: 4246909 bytes, checksum: 19c74f241fc5b3a706f6c977c778131d (MD5) Previous issue date: 2016-03-01 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Com a grande visibilidade e avanços que a área médica recebe, esta necessita de grande investimento para adquirir equipamentos sofisticados, porém existem materiais comumente encontrados no dia a dia que se destacam para aplicação no ramo medicinal devido suas propriedades satisfatórias e principalmente o baixo custo. Um desses materiais são os hidrogéis, nos quais são polímeros altamente hidrofílicos que quando obtidos por meio de fontes naturais possuem características atrativas para utilização nesta área. A combinação de hidrogéis com nanoestruturas resulta na produção de nanocompósitos que são materiais promissores para o uso em sistemas que necessitam de processo de liberação controlada. Tais sistemas têm o intuito de aumentar o tempo de liberação seja do fármaco, pesticida, água, fertilizante e minimizar perdas expressivas. Com isso, a proposta do trabalho é desenvolver e caracterizar hidrogéis nanocompósitos a base de polissacarídeos para possível utilização como veículos carreadores em sistemas de liberação controlada de fármacos. Os hidrogéis foram obtidos gotejando controladamente a solução de alginato de sódio e alginato de sódio com nanocargas em diferentes concentrações de cloreto de cálcio (CaCl2) ou cloreto de alumínio (AlCl3). Para caracterização, as propriedades hidrofílicas foram determinadas por medidas de grau de intumescimento, as morfológicas e espectroscópicas foram avaliadas por meio das técnicas de Espectroscopia de Absorção no Infravermelho com Transformada de Fourier (FTIR) e Microscopia Eletrônica de Varredura (MEV) acoplada a EDX (Espectroscopia de Energia Dispersiva de Raios-X), respectivamente. Além disso, as propriedades térmicas foram estudadas por meio de Análise Termogravimétrica (TG); e por fim a técnica de Difração de Raios-X foi utilizada para determinar a propriedade estrutural e o grau de intercalação da nanoargila. Com base nos resultados obtidos foi possível determinar a concentração ideal do polissacarídeo, o melhor agente reticulador e a nanocarga que melhor se adequou a matriz do hidrogel. As análises de MEV, EDX e FTIR confirmam a incorporação e a boa dispersão da nanocarga nos hidrogéis. Além disso, a nanoargila melhorou a estabilidade térmica dos hidrogéis. Os resultados demonstraram que os hidrogéis nanocompósitos a base de polissacarídeo podem ser considerados materiais promissores em sistemas de liberação controlada como carreadores de fármacos. / With the high visibility and advances in the medical field, needing that high investment to get sophisticated equipments, however there are materials generally found daily that stand out for application in the medical field due its satisfactory properties and mainly the low cost. One of these materials is the hydrogels, which are highly hydrophilic polymers that when obtained from natural sources have attractive characteristics for use in this field. The combination of hydrogels with nanofillers , i.e., nanoclay and zeolite, result in the production of promising nanocomposites for the use in system that require of controlled release process. Such systems have objective to increase the release time of drug, pesticide, water, fertilizer and minimize the significant losses. Thus, the proposal of this study is to develop and characterize nanocomposite hydrogels based on polysaccharide for possible utilization as carrier vehicles in controlled release systems of drugs. The hydrogels were obtained dripping controllably the sodium alginate and sodium alginate with nanofillers solutions in different concentration of calcium chloride and aluminum chloride. Hydrophilic properties were determined by degree of swelling measurements, and the morphological and spectroscopic were evaluated by means of techniques Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) coupled with EDX (Energy Dispersive X-ray spectroscopy). In addition, the thermal properties were studied using the Thermogravimetric Analysis (TGA); and finally the X-ray diffraction technique was used to determine the structural property and the degree of interleaving of nanoclay. Based on the results, it was possible to determine the optimal concentration of polysaccharide, the best crosslinking agent and the nanofiller that best suited the hydrogel matrix. The SEM and EDS analyzes and FTIR technique confirmed the incorporation and good dispersion of the nanoclay in the hydrogels. Furthermore, the nanoclay improved thermal stability of hydrogels. The results showed that the polysaccharide-based nanocomposite hydrogels can be considered as promising materials for controlled release systems as carriers of drugs. / CNPq: 132357/2014-3

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-18Bitstream added on 2014-06-13T18:53:39Z : No. of bitstreams: 1 arlindo_eps_me_ilha.pdf: 3403830 bytes, checksum: 35e9bb51a7710370f78852b7519f78ec (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nanocompósitos são materiais que combinam duas (ou mais) fases sólidas, uma das quais deve possuir dimensões nanométricas, que pode reunir em um único material várias propriedades melhoradas para uma dada aplicação e, portanto, podem permitir a coexistência de propriedades tradicionalmente antagônicas como, transparência e condutividade. O presente trabalho teve como objetivo a obtenção de um nanocompósito polimérico transparente e condutor de polimetilmetacrilato – PMMA com nanofitas do sistema Indium Tin Oxide – ITO. Para isto primeiramente estudou-se a influência da temperatura na síntese das nanoestruturas de ITO e depois de obtida a temperatura de síntese que proporcionou o crescimento de nanofitas de ITO com maior condutividade e maior transparência no espectro visível, estudou-se a influência da inserção destas nanofitas nas propriedades ópticas e elétricas de filmes nanocompósitos de PMMA. Como as nanofitas obtidas são emaranhadas, para a obtenção do nanocompósito foi realizada uma separação prévia das mesmas utilizando duas dispersões distintas: sendo a primeira em um ultrasom convencional e a segunda em uma ponta ultrasônica. Depois de dispersas, as nanofitas foram misturadas ao PMMA comercial dissolvido em concentrações mássicas de 1%, 2%, 5% e 10% de nanofitas. As soluções foram então depositadas sobre substrato de vidro e, depois de secos, os filmes foram destacados. As caracterizações ópticas mostraram que a transmitância no espectro visível dos filmes diminui em função do aumento da quantidade de nanofitas no compósito. Neste estudo, as caracterizações elétricas mostraram que ocorreu percolação das nanofitas no polímero após a inserção de 5% em massa de nanofitas. As imagens de MET para os filmes corroboraram os resultados previstos pelas caracterizações elétricas. Os filmes... / Nanocomposites are materials which have two or more solid phases, and one of these phases should be in nano-sized scale range. These materials can have several properties increased for special application and it is possible to obtain composites with traditionally antagonistic combinations of properties, such as transparence in the visible range of light and good conductivity. The main goal of this work is obtain a transparent and conductive polymer-based nanocomposite using polymethylmethacrylate – PMMA and ITO (Indium Tin Oxide) nanobelts. To reach this goal it was first studied the influence of temperature on the synthesis of nanostructured ITO. Once the temperature of synthesis was optimized to ensure the growth of ITO nanobelts with both good conductivity and good transparency in the visible spectrum, we studied the influence of ITO nanobelts on the electrical and optical properties of nanocomposites of PMMA. Because the synthesized nanobelts are entangled each other, to obtain the composite it was realized a separation of them using two different ways; first using a conventional ultrasound and after an ultrasonic tip. Then, nanobelts were mixed with commercial PMMA dissolved in THF 10% in mass concentrations of 1%, 2%, 5% and 10%. So, the solution was deposited over a glass substrate by casting. The results showed that films transmittance in visible range decreases by increasing the amount of nanobelts. The electrical characterization showed that percolation occurred after 5%wt of filler. TEM images of composites corroborate the results provided by the electrical measures. The films prepared using both dispersions had the same transmittance in the visible spectrum, despite of the films obtained by dispersing the nanobelts in ultrasonic tip had a lower electrical resistance. Thus it can be concluded that the dispersion by ultrasonic... (Summary complete electronic access click below)

abstract: With the maturity of advanced composites as feasible structural materials for various applications there is a critical need to solve the challenge of designing these material systems for optimal performance. However, determining superior design methods requires a deep understanding of the material-structure properties at various length scales. Due to the length-scale dependent behavior of advanced composites, multiscale modeling techniques may be used to describe the dominant mechanisms of damage and failure in these material systems. With polymer matrix fiber composites and nanocomposites it becomes essential to include even the atomic length scale, where the resin-hardener-nanofiller molecules interact, in the multiscale modeling framework. Additionally, sources of variability are also critical to be included in these models due to the important role of uncertainty in advance composite behavior. Such a methodology should be able to describe length scale dependent mechanisms in a computationally efficient manner for the analysis of practical composite structures. In the research presented in this dissertation, a comprehensive nano to macro multiscale framework is developed for the mechanical and multifunctional analysis of advanced composite materials and structures. An atomistically informed statistical multiscale model is developed for linear problems, to estimate and scale elastic properties of carbon fiber reinforced polymer composites (CFRPs) and carbon nanotube (CNT) enhanced CFRPs using information from molecular dynamics simulation of the resin-hardener-nanofiller nanoscale system. For modeling inelastic processes, an atomistically informed coupled damage-plasticity model is developed using the framework of continuum damage mechanics, where fundamental nanoscale covalent bond disassociation information is scaled up as a continuum scale damage identifying parameter. This damage model is coupled with a nanocomposite microstructure generation algorithm to study the sub-microscale damage mechanisms in CNT/CFRP microstructures. It is further integrated in a generalized method of cells (GMC) micromechanics model to create a low-fidelity computationally efficient nonlinear multiscale method with imperfect interfaces between the fiber and matrix, where the interface behavior is adopted from nanoscale MD simulations. This algorithm is used to understand damage mechanisms in adhesively bonded composite joints as a case study for the comprehensive nano to macroscale structural analysis of practical composites structures. At each length scale sources of variability are identified, characterized, and included in the multiscale modeling framework. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2018

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-07-12T10:48:17Z No. of bitstreams: 1 JOÃO EMÍDIO DA SILVA NETO - DISSERTAÇÃO (PPGCEMat) 2015.pdf: 4756921 bytes, checksum: 06e32a45828b2df2ef5a64d06f2272b8 (MD5) / Made available in DSpace on 2018-07-12T10:48:17Z (GMT). No. of bitstreams: 1 JOÃO EMÍDIO DA SILVA NETO - DISSERTAÇÃO (PPGCEMat) 2015.pdf: 4756921 bytes, checksum: 06e32a45828b2df2ef5a64d06f2272b8 (MD5) Previous issue date: 2015-02-09 / CNPq / Neste trabalho, utilizando a técnica de intercalação por fusão, foram preparados híbridos à base de polipropileno homopolímero com 5% em peso de argila bentonítica organofílica, compatibilizante polipropileno enxertado com anidrido maleico em teores de 5 e 15%, e co-intercalante erucamida em teores de 0,5 e 1,0%. Os sistemas foram processados em misturador interno e extrusora dupla rosca corrotacional interpenetrante, sob uma única condição de processamento. Os híbridos foram caracterizados por índice de fluidez (MFI), calorimetria exploratória diferencial (DSC), termogravimetria (TG), difração de raios-X (DRX), microscopia óptica, microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET) e propriedades mecânicas em tração e impacto. Os resultados de índice de fluidez evidenciaram a redução deste parâmetro com a adição da argila e/ou aditivos (compatibilizante e co-intercalante), indicando aumento da viscosidade nos sistemas. Por DSC e TG foi possível observar que a presença da argila e do agente compatibilizante elevou a estabilidade térmica dos materiais quando comparados ao polipropileno puro. Os resultados de difração de raios X mostraram aumento da distância interplanar basal d(001) dos sistemas, formando estruturas intercaladas, em especial nas composições em que o agente co-intercalante foi empregado. A resistência à tração dos sistemas não foi afetada significativamente, mas foi observado um aumento no módulo de elasticidade e na resistência ao impacto com a incorporação dos compatibilizantes. A microscopia eletrônica de transmissão revelou a formação de nanocompósitos com estruturas parcialmente esfoliadas e/ou intercaladas. / In this work, hybrids of polypropylene homopolymer containing 5% by weight organoclay, 5 and 15% maleic anhydride grafted polypropylene and 0.5 and 1.0% erucamide, respectively, were prepared by melt intercalation. The systems were processed in an internal mixer and corotating twin screw extruder, at a single processing condition. The hybrids were characterized by melt flow index (MFI), differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile and impact properties. Melt flow rate results showed a decrease in this parameter with clay and/or additives (compatibilizer and co-intercalant) addition, which indicates an increase in the system´s viscosity. DSC and TG, data suggested that the thermal stability of the systems increased with clay and coupling agent incorporation. X-ray diffraction results showed increased basal interplanar distance d(001) of the systems forming intercalated structures, in particular in compositions where the co-intercalating agent was utilized. The tensile strength of the systems was not significantly affected, however, an increase on elastic modulus and on impact resistance was observed with the additives incorporation. Transmission electron microscopy revealed the formation of partially exfoliated and/or intercalated nanocomposites.